Sporophyte Generation Research Articles

Unraveling metabolic mechanisms behind chloroplast desiccation tolerance: Chlorophyllous fern spore as a new promising unicellular model

Fern spores are unicellular structures produced by the sporophyte generation that give rise to the haploid gametophyte. When released from the sporangium, spores are desiccation tolerant (DT) in the royal fern (Osmunda regalis) and contain fully developed chloroplasts. As a consequence, this type of spores is called chlorophyllous spores (CS). Upon transfer to germination conditions, CS initiate a process of imbibition that suppresses DT in 72 h, before the germination starts. In parallel to such change in DT, thylakoids undergo a profound remodelling in composition and function. Firstly, sustained quenching of chlorophyll fluorescence is relaxed, giving rise to photochemically active CS, while lipid composition shifts from that of a resting structure to a metabolically active cell. Basically trigalactolipids decreased in favour of monogalactolipids, with a parallel desaturation of fatty acids. Storage lipids such as triacylglycerol were quickly depleted. These results highlight the importance of the structure of thylakoids lipid as a key to protect membrane integrity during desiccation, together with the saturation of fatty acids and the constitutive chlorophyll quenching to prevent oxidative damage. The CS used here, in which the same cell shifts from DT to sensitive strategy in 72 h, reveal their potential as unicellular models for future studies on DT.

In vitro completion of sexual life cycle—Production of next sporophytic generation through in vitro flowering and fruiting in Solanum americanum and Solanum villosum

An effective method for inducing high-frequency in vitro flowering and fruiting in two important medicinal species of Solanum (S. americanum and S. villosum) was standardized. In vitro multiplied shoots were cultured on MS media supplemented with 6-benzylaminopurine (BAP) alone or in combination with silver thiosulphate (STS). Synergism between STS and BAP improved flower induction. Flowering frequency enriched significantly when the duration between two sub-cultures was prolonged and strength of the MS medium increased 1.5 fold. Highest response, with total 36.7 ± 0.42 (S. americanum) and 33.2 ± 0.34 (S. villosum) flowers per plant were induced within 90 days of culture in the medium containing 0.35 mg L−1 BAP and 40 μM STS. Maximum of 19 flowers bloomed together at a time in a single plant grown in a 250 ml conical flask. The increased concentration of sucrose (5.0%) in the medium and in vitro hand-pollination enhanced frequency of fruit setting. All flowers and fruits were normal in size and color as compared to in vivo plants. Along with maturation, the green fruits were turn to blackish-purple (S. americanum) or reddish-orange (S. villosum) containing 11 ± 0.52 or 18 ± 0.67 seeds per fruit, respectively. On an average, 94 ± 2.8 and 98 ± 3.1 days were required, respectively, for the completion of sexual lifecycle from shoot implantation up to germination of in vitro derived seeds produced via in vitro flowering and fruit ripening. The germination frequencies of in vitro produced seeds were 86.4 ± 2.1% (S. americanum) to 94.5 ± 2.5% (S. villosum). The present protocol has standardized a group of factors that regulates in vitro flowering, fruiting, and seed setting. This in vitro method offers a repeatable system for studying the physiological mechanism of flowering and fruiting in controlled environment and can assist improvement of other related Solanaceous crops through fast-track in vitro cross-breeding programs throughout the year without depending on season.

A Survey of MIKC Type MADS-Box Genes in Non-seed Plants: Algae, Bryophytes, Lycophytes and Ferns.

MADS box transcription factors have been studied extensively in flowering plants but remain less studied in non-seed plants. MADS box is one such example of a gene which is prevalent across many classes of plants ranging from chlorophyta to embryophyta as well as fungi and animals. MADS box transcription factors are of two types, Type I and Type II. Type II transcription factors (TF) that consist of a MADS domain, I region, K domain, and C terminal domain are discussed in this review. The Type II/ MIKC class is widespread across charophytes and all major lineages of land plants but unknown in green and red algae. These transcription factors have been implicated in floral development in seed plants and thus the question arises, “What is their role in non-seed plants?” From the studies reviewed here it can be gathered that unlike seed plants, MIKCC genes in non-seed plants have roles in both gametophytic and sporophytic generations and contribute to the development of both vegetative and reproductive structures. On the other hand as previously observed in seed plants, MIKC* genes of non-seed plants have a conserved role during gametophyte development. With respect to evolution of MIKC genes in non-seed plants, the number of common ancestors is probably very few at each branch. The expansion of this gene family in seed plants and increased plant complexity seem to be correlated. As gradually the genomes of non-seed plants are becoming available it is worthwhile to gather the existing information about MADS box genes in non-seed plants. This review highlights various MIKC MADS box genes discovered so far in non-seed plants, their possible roles and an insight into their evolution.

Extensive epigenetic reprogramming during the life cycle of Marchantia polymorpha.

BackgroundIn plants, the existence and possible role of epigenetic reprogramming has been questioned because of the occurrence of stably inherited epialleles. Evidence suggests that epigenetic reprogramming does occur during land plant reproduction, but there is little consensus on the generality and extent of epigenetic reprogramming in plants. We studied DNA methylation dynamics during the life cycle of the liverwort Marchantia polymorpha. We isolated thalli and meristems from male and female gametophytes, archegonia, antherozoids, as well as sporophytes at early and late developmental stages, and compared their DNA methylation profiles.ResultsOf all cytosines tested for differential DNA methylation, 42% vary significantly in their methylation pattern throughout the life cycle. However, the differences are limited to few comparisons between specific stages of the life cycle and suggest four major epigenetic states specific to sporophytes, vegetative gametophytes, antherozoids, and archegonia. Further analyses indicated clear differences in the mechanisms underlying reprogramming in the gametophytic and sporophytic generations, which are paralleled by differences in the expression of genes involved in DNA methylation. Differentially methylated cytosines with a gain in methylation in antherozoids and archegonia are enriched in the CG and CHG contexts, as well as in gene bodies and gene flanking regions. In contrast, gain of DNA methylation during sporophyte development is mostly limited to the CHH context, LTR retrotransposons, DNA transposons, and repeats.ConclusionWe conclude that epigenetic reprogramming occurs at least twice during the life cycle of M. polymorpha and that the underlying mechanisms are likely different between the two events.

Evolution of the seed habit: Is niche construction a missing component?

Evolution of land plants is one of the major transitions in the history of life on Earth. In this process, evolution of seeds constitutes one of the key events, liberating plants from dependence of free external water for fertilization, thus promoting colonization of dry environments and the build-up of terrestrial ecosystems. Previous explanations of evolution of seeds from heterosporous predecessors have been based on a framework of kin and sexual selection theory. Here I suggest that that niche construction is a missing component in these explanations. During colonization of increasingly drier habitats, the heterosporous life cycle was subjected to strong gradients in water availability. The ancestral condition of separate niches of the sporophyte and female gametophyte generations changed into a situation where the sporophyte generation provided the only means by which female gametophytes could develop, in effect ‘constructing’ the recruitment niche for the female gametophyte, attached to the sporophyte. Selection favored modifications in the developmental program, altering the relative timing of fertilization and dispersal. Kin and sexual selection processes could then play out in the context of a plant life cycle where fertilization preceded dispersal, eventually forming the seed habit. Niche construction by the sporophyte removed the ecological independence of the two generations; the sporophyte provided the female gametophyte with a recruitment niche, transforming the biphasic life cycle into a unitary life cycle, and enabled an expansion of the ecological niche zone for land plants, eventually leading to a vegetation covering most parts of the land mass.

The enigma of sex allocation in Selaginella.

The division of resource investment between male and female functions is poorly known for land plants other than angiosperms. The ancient lycophyte genus Selaginella is similar in some ways to angiosperms (in heterospory and in having sex allocation occur in the sporophyte generation, for example) but lacks the post-fertilization maternal investments that angiosperms make via fruit and seed tissues. One would therefore expect Selaginella to have sex allocation values less female-biased than in flowering plants and closer to the theoretical prediction of equal investment in male and female functions. Nothing is currently known of sex allocation in the genus, so even the simplest predictions have not been tested. Volumetric measurements of microsporangial and megasporangial investment were made in 14 species of Selaginella from four continents. In five of these species the length of the main above-ground axis of each plant was measured to determine whether sex allocation is related to plant size. Of the 14 species, 13 showed male-biased allocations, often extreme, in population means and among the great majority of individual plants. There was some indication from the five species with axis length measurements that relative male allocation might be related to the release height of spores, but this evidence is preliminary. Sex allocation in Selaginella provides a phylogenetic touchstone showing how the innovations of fruit and seed investment in the angiosperm life cycle lead to typically female-biased allocations in that lineage. Moreover, the male bias we found in Selaginella requires an evolutionary explanation. The bias was often greater than what would occur from the mere absence of seed and fruit investments, and thus poses a challenge to sex allocation theory. It is possible that differences between microspores and megaspores in their dispersal ecology create selective effects that favour male-biased sexual allocation. This hypothesis remains tentative.

DISTAG/TBCCd1 Is Required for Basal Cell Fate Determination in Ectocarpus.

Brown algae are one of the most developmentally complex groups within the eukaryotes. As in many land plants and animals, their main body axis is established early in development, when the initial cell gives rise to two daughter cells that have apical and basal identities, equivalent to shoot and root identities in land plants, respectively. We show here that mutations in the Ectocarpus DISTAG (DIS) gene lead to loss of basal structures during both the gametophyte and the sporophyte generations. Several abnormalities were observed in the germinating initial cell in dis mutants, including increased cell size, disorganization of the Golgi apparatus, disruption of the microtubule network, and aberrant positioning of the nucleus. DIS encodes a TBCCd1 protein, which has a role in internal cell organization in animals, Chlamydomonas reinhardtii, and trypanosomes. Our study highlights the key role of subcellular events within the germinating initial cell in the determination of apical/basal cell identities in a brown alga and emphasizes the remarkable functional conservation of TBCCd1 in regulating internal cell organization across extremely distant eukaryotic groups.

Arabidopsis LORELEI, a Maternally Expressed Imprinted Gene, Promotes Early Seed Development.

In flowering plants, the female gametophyte controls pollen tube reception immediately before fertilization and regulates seed development immediately after fertilization, although the controlling mechanisms remain poorly understood. Previously, we showed that LORELEI (LRE), which encodes a putative glycosylphosphatidylinositol-anchored membrane protein, is critical for pollen tube reception by the female gametophyte before fertilization and the initiation of seed development after fertilization. Here, we show that LRE is expressed in the synergid, egg, and central cells of the female gametophyte and in the zygote and proliferating endosperm of the Arabidopsis (Arabidopsis thaliana) seed. Interestingly, LRE expression in the developing seeds was primarily from the matrigenic LRE allele, indicating that LRE expression is imprinted. However, LRE was biallelically expressed in 8-d-old seedlings, indicating that the patrigenic allele does not remain silenced throughout the sporophytic generation. Regulation of imprinted LRE expression is likely novel, as LRE was not expressed in pollen or pollen tubes of mutants defective for MET1, DDM1, RNA-dependent DNA methylation, or MSI-dependent histone methylation. Additionally, the patrigenic LRE allele inherited from these mutants was not expressed in seeds. Surprisingly, and contrary to the predictions of the parental conflict hypothesis, LRE promotes growth in seeds, as loss of the matrigenic but not the patrigenic LRE allele caused delayed initiation of seed development. Our results showed that LRE is a rare imprinted gene that functions immediately after double fertilization and supported the model that a passage through the female gametophyte establishes monoalleleic expression of LRE in seeds and controls early seed development.

Оцінка стійкості ліній перцю солодкого (Capsicum Annuum L.) до фузаріозного в’янення на рівні культури in vitro та in vivo

Оцінка стійкості ліній перцю солодкого (Capsicum Annuum L.) до фузаріозного в’янення на рівні культури in vitro та in vivo

Short-range dispersal maintains a volatile marine metapopulation: the brown alga Postelsia palmaeformis.

The annual brown alga Postelsia palmaeformis is dependent for its survival on short-distance dispersal (SDD) where it is already established, as well as occasional long-distance colonization of novel sites. To quantify SDD, we transplanted Postelsia to sites lacking established plants within ≥10m. The spatial distribution of the first naturally produced sporophyte generation was used to fit dispersal kernels in a hierarchical Bayesian framework. Mean dispersal distance within a year ranged from 0.16 to 0.50m across sites; 95% of the recruits were within 0.38-1.32m of the transplant. The fat-tailed exponential square root kernel was the best among the candidate models at describing offspring density and dispersal. Independent measurements of patch size over two to five generations permitted an evaluation of whether models parameterized by individual-level data could adequately predict longer-term persistence and spread at the patch scale. The observed spread rates generally fell within the 95% predictive intervals. Finally, Postelsia was eliminated from 14 occupied sites that were then followed for ≥27yr. The probability of invasion when unoccupied declined and the probability of extinction when occupied increased with distance from the nearest propagule source. Sites >10m from a source were rarely invaded, and one initially densely populated site isolated by 39m has remained Postelsia-free since 1981. In spite of dispersal that is almost entirely within 2m of the parent, the ability of our models to capture the observed dynamics of Postelsia indicates that short-range dispersal adequately explains the persistent and thriving Postelsia metapopulation on Tatoosh Island. However, the presence of Postelsia over a 2000-km coastal range with many gaps >1km makes it clear that rare long-distance dispersal must be required to explain the geographic range of the species.

The Separation of Generations: Biology and Biogeography of Long-Lived Sporophyteless Fern Gametophytes

Premise of research. Ferns (monilophytes) and lycophytes are unique among land plants in having two independent life stages: the gametophyte generation, which is generally small, cordiform, and short-lived, senescing after fertilization, and the sporophyte generation, which is considered the dominant, long-lived portion of the life cycle produced following fertilization. In many species of epiphytic ferns, however, the gametophyte generation is capable of sustained vegetative growth, and some are able to reproduce asexually via gemmae. These two characteristics have increased the independence of these gametophytes, so much so that some species never produce sporophytes at all, while other species produce sporophytes only in parts of their geographic range, a trend we term here the “separation of generations.”Pivotal results. Long-lived fern gametophytes have evolved independently in several families and can be found around the world. We present a comprehensive review of the long-lived fern gametophytes th...

The Ectocarpus IMMEDIATE UPRIGHT gene encodes a member of a novel family of cysteine-rich proteins with an unusual distribution across the eukaryotes.

The sporophyte generation of the brown alga Ectocarpus sp. exhibits an unusual pattern of development compared with the majority of brown algae. The first cell division is symmetrical and the apical-basal axis is established late in development. In the immediate upright (imm) mutant, the initial cell undergoes an asymmetric division to immediately establish the apical-basal axis. We provide evidence which suggests that this phenotype corresponds to the ancestral state of the sporophyte. The IMM gene encodes a protein of unknown function that contains a repeated motif also found in the EsV-1-7 gene of the Ectocarpus virus EsV-1. Brown algae possess large families of EsV-1-7 domain genes but these genes are rare in other stramenopiles, suggesting that the expansion of this family might have been linked with the emergence of multicellular complexity. EsV-1-7 domain genes have a patchy distribution across eukaryotic supergroups and occur in several viral genomes, suggesting possible horizontal transfer during eukaryote evolution.

Marchantia MpRKD Regulates the Gametophyte-Sporophyte Transition by Keeping Egg Cells Quiescent in the Absence of Fertilization

Unlike in animals, the life cycle of land plants alternates between two multicellular generations, the haploid gametophyte and the diploid sporophyte [1]. Gamete differentiation initiates the transition from the gametophyte to the sporophyte generation and, upon maturation, the egg cell establishes a quiescent state that is maintained until fertilization. This quiescence represents a hallmark of the gametophyte-sporophyte transition. The underlying molecular mechanisms are complex and best characterized in the flowering plant Arabidopsis thaliana [2-4]. However, only few genes with egg cell-specific expression or defects have been identified [5-10]. Intriguingly, ectopic expression of members of a clade of RWP-RK domain (RKD)-containing transcription factors, which are absent from animal genomes [11-13], can induce an egg cell-like transcriptome in sporophytic cells of A.thaliana. Yet, to date, loss-of-function experiments have not produced phenotypes affecting the egg cell, likely due to genetic redundancy and/or cross-regulation among the five RKD genes of A.thaliana [10]. To reduce genetic complexity, we explored the genome of Marchantia polymorpha, a liverwort belonging to the basal lineage of extant land plants [14-17]. Based on sequence homology, we identified a single M.polymorpha RKD gene, MpRKD, which is orthologous to all five A.thaliana RKD genes. Analysis of the MpRKD expression pattern and characterization of lines with reduced MpRKD activity indicate that it functions as a regulator of gametophyte development and the gametophyte-sporophyte transition. In particular, MpRKD is required to establish and/or maintain the quiescent state of the egg cell in the absence of fertilization.

Cross-Talk Between Sporophyte and Gametophyte Generations Is Promoted by CHD3 Chromatin Remodelers inArabidopsis thaliana

Angiosperm reproduction requires the integrated development of multiple tissues with different genotypes. To achieve successful fertilization, the haploid female gametophytes and diploid ovary must coordinate their development, after which the male gametes must navigate through the maternal sporophytic tissues to reach the female gametes. After fertilization, seed development requires coordinated development of the maternal diploid integuments, the triploid endosperm, and the diploid zygote. Transcription and signaling factors contribute to communication between these tissues, and roles for epigenetic regulation have been described for some of these processes. Here we identify a broad role for CHD3 chromatin remodelers in Arabidopsis thaliana reproductive development. Plants lacking the CHD3 remodeler, PICKLE, exhibit various reproductive defects including abnormal development of the integuments, female gametophyte, and pollen tube, as well as delayed progression of ovule and embryo development. Genetic analyses demonstrate that these phenotypes result from loss of PICKLE in the maternal sporophyte. The paralogous gene PICKLE RELATED 2 is preferentially expressed in the endosperm and acts antagonistically with respect to PICKLE in the seed: loss of PICKLE RELATED 2 suppresses the large seed phenotype of pickle seeds. Surprisingly, the alteration of seed size in pickle plants is sufficient to determine the expression of embryonic traits in the seedling primary root. These findings establish an important role for CHD3 remodelers in plant reproduction and highlight how the epigenetic status of one tissue can impact the development of genetically distinct tissues.

Evolutionary analysis of iron (Fe) acquisition system in Marchantia polymorpha.

To acquire appropriate iron (Fe), vascular plants have developed two unique strategies, the reduction-based strategy I of nongraminaceous plants for Fe(2+) and the chelation-based strategy II of graminaceous plants for Fe(3+) . However, the mechanism of Fe uptake in bryophytes, the earliest diverging branch of land plants and dominant in gametophyte generation is less clear. Fe isotope fractionation analysis demonstrated that the liverwort Marchantia polymorpha uses reduction-based Fe acquisition. Enhanced activities of ferric chelate reductase and proton ATPase were detected under Fe-deficient conditions. However, M.polymorpha did not show mugineic acid family phytosiderophores, the key components of strategy II, or the precursor nicotianamine. Five ZIP (ZRT/IRT-like protein) homologs were identified and speculated to be involved in Fe uptake in M.polymorpha. MpZIP3 knockdown conferred reduced growth under Fe-deficient conditions, and MpZIP3 overexpression increased Fe content under excess Fe. Thus, a nonvascular liverwort, M.polymorpha, uses strategy I for Fe acquisition. This system may have been acquired in the common ancestor of land plants and coopted from the gametophyte to sporophyte generation in the evolution of land plants.

Class III HD-Zip activity coordinates leaf development in Physcomitrella patens

Land plant bodies develop from meristems, groups of pluripotent stem cells, which may persist throughout the life of a plant or, alternatively, have a transitory existence. Early diverging land plants exhibit indeterminate (persistent) growth in their haploid gametophytic generation, whereas later diverging lineages exhibit indeterminate growth in their diploid sporophytic generation, raising the question of whether genetic machinery directing meristematic functions was co-opted between generations. Class III HD-Zip (C3HDZ) genes are required for the establishment and maintenance of shoot apical meristems in flowering plants. We demonstrate that in the moss Physcomitrella patens, C3HDZ genes are expressed in transitory meristems in both the gametophytic and sporophytic generations, but not in the persistent shoot meristem of the gametyphyte. Loss-of-function of P. patens C3HDZ was engineered using ectopic expression of miR166, an endogenous regulator of C3HDZ gene activity. Loss of C3HDZ gene function impaired the function of gametophytic transitory meristematic activity but did not compromise the functioning of the persistent shoot apical meristem during the gametophyte generation. These results argue against a wholesale co-option of meristematic gene regulatory networks from the gametophyte to the sporophyte during land plant evolution, instead suggesting that persistent meristems with a single apical cell in P. patens and persistent complex meristems in flowering plants are regulated by different genetic programs.

The Pseudoautosomal Regions of the U/V Sex Chromosomes of the Brown Alga Ectocarpus Exhibit Unusual Features.

The recombining regions of sex chromosomes (pseudoautosomal regions, PARs) are predicted to exhibit unusual features due to their being genetically linked to the nonrecombining, sex-determining region. This phenomenon is expected to occur in both diploid (XY, ZW) and haploid (UV) sexual systems, with slightly different consequences for UV sexual systems because of the absence of masking during the haploid phase (when sex is expressed) and because there is no homozygous sex in these systems. Despite a considerable amount of theoretical work on PAR genetics and evolution, these genomic regions have remained poorly characterized empirically. We show here that although the PARs of the U/V sex chromosomes of the brown alga Ectocarpus recombine at a similar rate to autosomal regions of the genome, they exhibit many genomic features typical of nonrecombining regions. The PARs were enriched in clusters of genes that are preferentially, and often exclusively, expressed during the sporophyte generation of the life cycle, and many of these genes appear to have evolved since the Ectocarpales diverged from other brown algal lineages. A modeling-based approach was used to investigate possible evolutionary mechanisms underlying this enrichment in sporophyte-biased genes. Our results are consistent with the evolution of the PAR in haploid systems being influenced by differential selection pressures in males and females acting on alleles that are advantageous during the sporophyte generation of the life cycle.

Glyphosate Susceptibility of Different Life Stages of Three Fern Species

Abstract Glyphosate, a systemic herbicide, is used against weeds in agricultural fields as well as against invasive plants in pastures, forest plantations, and urban environments. Its frequent and widespread use can negatively impact the surrounding natural non-target vegetation following the accidental drift of spray droplets, leaching, or persistence as residues in the soil. Because ferns possess a life cycle with independent sporophytic and gametophytic generations, herbicides may cause a different impact on each life stage. The objective of the present study was to evaluate the effect of four concentrations of glyphosate (0.33, 0.65, 2.72, and 10.89 g active ingredient L-1) and water as control treatments on spores, gametophytes, and two sporophyte size classes of one native (Blechnum appendiculatum Willd.) and two introduced fern species in Mexico (Macrothelypteris torresiana (Gaudich.) Ching and Thelypteris dentata (Forssk.) E.P. St.John). Spore germination was evaluated 10 days after herbicide trea...

Molecular Genetic Tools and Techniques for Marchantia polymorpha Research.

Liverworts occupy a basal position in the evolution of land plants, and are a key group to address a wide variety of questions in plant biology. Marchantia polymorpha is a common, easily cultivated, dioecious liverwort species, and is emerging as an experimental model organism. The haploid gametophytic generation dominates the diploid sporophytic generation in its life cycle. Genetically homogeneous lines in the gametophyte generation can be established easily and propagated through asexual reproduction, which aids genetic and biochemical experiments. Owing to its dioecy, male and female sexual organs are formed in separate individuals, which enables crossing in a fully controlled manner. Reproductive growth can be induced at the desired times under laboratory conditions, which helps genetic analysis. The developmental process from a single-celled spore to a multicellular body can be observed directly in detail. As a model organism, molecular techniques for M. polymorpha are well developed; for example, simple and efficient protocols of Agrobacterium-mediated transformation have been established. Based on them, various strategies for molecular genetics, such as introduction of reporter constructs, overexpression, gene silencing and targeted gene modification, are available. Herein, we describe the technologies and resources for reverse and forward genetics in M. polymorpha, which offer an excellent experimental platform to study the evolution and diversity of regulatory systems in land plants.

Construction of a high density SNP linkage map of kelp (Saccharina japonica) by sequencing Taq I site associated DNA and mapping of a sex determining locus.

BackgroundKelp (Saccharina japonica) has been intensively cultured in China for almost a century. Its genetic improvement is comparable with that of rice. However, the development of its molecular tools is extremely limited, thus its genes, genetics and genomics. Kelp performs an alternative life cycle during which sporophyte generation alternates with gametophyte generation. The gametophytes of kelp can be cloned and crossed. Due to these characteristics, kelp may serve as a reference for the biological and genetic studies of Volvox, mosses and ferns.ResultsWe constructed a high density single nucleotide polymorphism (SNP) linkage map for kelp by restriction site associated DNA (RAD) sequencing. In total, 4,994 SNP-containing physical (tag-defined) RAD loci were mapped on 31 linkage groups. The map expanded a total genetic distance of 1,782.75 cM, covering 98.66% of the expected (1,806.94 cM). The length of RAD tags (85 bp) was extended to 400–500 bp with Miseq method, offering us an easiness of developing SNP chips and shifting SNP genotyping to a high throughput track. The number of linkage groups was in accordance with the documented with cytological methods. In addition, we identified a set of microsatellites (99 in total) from the extended RAD tags. A gametophyte sex determining locus was mapped on linkage group 2 in a window about 9.0 cM in width, which was 2.66 cM up to marker_40567 and 6.42 cM down to marker_23595.ConclusionsA high density SNP linkage map was constructed for kelp, an intensively cultured brown alga in China. The RAD tags were also extended so that a SNP chip could be developed. In addition, a set of microsatellites were identified among mapped loci, and a gametophyte sex determining locus was mapped. This map will facilitate the genetic studies of kelp including for example the evaluation of germplasm and the decipherment of the genetic bases of economic traits.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1371-1) contains supplementary material, which is available to authorized users.